AME8855ACHT080 datasheet(12/34 Pages) AME

12 / 34 page

AME

High PSRR, Low Noise, 600mA

CMOS Regulator

AME8855A

Rev. B.02

The AME8855 family of CMOS regulators contain a

PMOS pass transistor, voltage reference, error amplifier,

over-current protection thermal shutdown, and Power Good

detection circuitry.

The P-channel pass transistor receives data from the

error amplifier, over-current shutdown, and thermal pro-

tection circuits. During normal operation, the error ampli-

fier compares the output voltage to a precision reference.

Over-current and Thermal shutdown circuits become ac-

tive when the junction temperature exceeds 150oC, or

the current exceeds 600mA. During thermal shutdown,

the output voltage remains low. Normal operation is re-

stored when the junction temperature drops more 20oC.

Capacitor Selection and Regulator Stability

The AME8855 is stable with an output capacitor to

ground of 1

µF or greater. Ceramic capacitors have the

lowest ESR, and will offer the best AC performance. Con-

versely, Aluminum Electrolytic capacitors exhibit the high-

est ESR, resulting in the poorest AC response. Unfortu-

nately, large value ceramic capacitors are comparatively

expensive. One option is to parallel a 0.1

µF ceramic

capacitor with a 10

µF Aluminum Electrolytic. The benefit

is low ESR, high capacitance, and low overall cost.

A second capacitor is recommended between the in-

put and ground to stabilize V

IN. The input capacitor should

be at least 0.1

µF to have a beneficial effect.

Enable Pin

The Enable Pin is pull-low. When activated pulled low,

the MOS pass transistor shuts off, and all internal cir-

cuits are powered down. In this state, the stand by cur-

rent is less than 1

µA.

n Detailed Description

Capacitor Selection and Regulator Stability

The maximum output power of the AME8855 is limited

by the maximum power dissipation of the package. By

calculation the power dissipation of the package as a

function of the input voltage, output voltage and output

current, the maximum input voltage can be obtained. The

maximum power dissipation should not exceed the

package

’s maximum power rating.

MAX = (V IN(MAX) -VOUT) x IOUT

Where:

IN(MAX) = maximum input voltage

MAX = maximum power dissipation of the package

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